Art of examining quartz



Dec. 2, 1941. H. w. N. HAWK ART OF EXAMINING QUARTZ Filed July 30, 1940 Patented Dec. 2, 1941 ART OF EXAMHN'IN G QUARTZ Henry w. N. Hawk, Merchantvillc, N. 1., assl nor to Radio Corporation of America, a corporation of Delaware Application July 30, 1940, Serial No. 348,603

5 Claims.

My present invention relates to theart of examining quartz of the type possessing piezoelectric properties and has for its principal object to provide an extremely simple and accurate method of simultaneously locating all three X-axes in imperfect quartz specimens, such, for example, as so-called river-bed quartz.

Another and important object of my invention is to provide a method of locating the X-axes in a quartz specimen and one which in its practice likewise discloses the electrical sense of polarity of the said axes and also the virtual location of the major and minor side and apex faces of the specimen.

My invention will be described in connection with the accompanying drawing, wherein Figure 1 is a partly pictorialview in perspective showing the first of two steps of a simple method of locating the X-axes in a piece of quartz,

Figure 2 is a magnified top plan View of the piece of quartz shown in Fig. 1 and which will be referred to in explaining the second step of the said method,

Figure 3 is a side partly'diagrammatic elevational view of an apparatus which may be employed in carrying out the improved method of my invention,

Figures 4 and 5 are plan views of quartz slabs whose major faces lie in planes normal to the optic (Z) axis and wherein the said faces have been inspected and marked with certain reference lines and characters as an aid in explaining the principle of my invention, and

Figure 6 is a view in perspective on a smaller scale of a quartz mother crystal.

Referring now to Fig. 1, I have observed that, if one forms a circular or spherical dent l'upon the surface of a quartz slab 2 whose top and bottom surfaces are perpendicular to the optic (Z) axis of the mother crystal, as by dropping a steel ball 3 thereon, and then polishes or grinds down the surface of the quartz adjacent the dent or point of impact, the dent I will assume a triangular pattern as shown at la in Fig. 2. The sides of this triangle la coincide substantially exactly with the three X-axes, Xi, X2, X3, of the mother crystal.

The above-described method of simultaneously locating the three X-axes in a quartz specimen, though an extremely simple one, is subject to several disadvantages, to wit: (a) the specimen may be shattered or seriously marred in forming a dent in its surface, (b) unless the dent spans a substantial surface area of the specimen, the

have to beextended (as indicated by the dotted lines, Fig. 2) by means of a ruler to give a readily discernable indication of the location of the X-axes, (c) this method does not reveal the polarity of the indicated X-axes.

I have now discovered that the pattern formed by a spot of light projected upon an etched surface of a quartz slab whose top and bottom surfaces lie in planes which are substantially normal to the optic (Z) axis not only reveals (a) all three X-axes of the specimen and (b) their p0- 1arlty,=but also (0) the virtual location of the major and minor side and apex faces of the mother crystal from which the specimen was obtained.

As above indicated, in carrying the invention into effect, it is first necessary to determine the location of the optical or Z-axis in the mother crystal or other specimen. This may be done by any known method. By ,way of example, the

mother crystal, if it is translucent or, alternatively', a translucent piece cut from any part of the mother crystal, may be immersed in cedar oil (or other substance having an index of refraction of the same general order as quartz) and examined by means of polarized-light whil rotating the specimen until the colored light patterns or rings which are characteristic of the Z-axis are observed. The Z-axis at that time lies along the line of sight of the observer. The location of the Z-axis havingbeen determined, a slab of any desired thickness is cut from the specimen in such a manner that the majorfaces of the slab lie in substantially parallel Planeswhich are substantially normal to the Z-axis.

Such a slab is designated 9 in Figs. 3, 4 and 5. It is then necessary to etch one of the principal surfaces of the slab 'as with a 48% solution of hydrofluoric acid for a period of, say, three or four hours. The best results are achieved when the opposite principal surface of the slab is polished, or, at least, not etched.

Any convenient spot source of light may be employed in inspecting the slab. In Fig. 3, there is shown, by way of example, an are light 5 provided with, a mask 6 containing a pin hole I- through which the light is projected upon the etched face 8 of the slab 9. The operator preferably observes the slab 9 from its unetched-or polished side i0. Obviously, however, the pattern may be projected on ascreen (not shown) if desired.

The pattern produced in or on the quartz slab by the spot source of light, as viewed by an-obsides of the resulting triangular pattern may 55 server (indicated by the eye in Fig. 3) looking in lines 12 n and n the direction of the source, through the unetched or polished surface of the slab, will, if the spot is small enough, be similar to that indicated by the solid lines H, II and II in Fig. 4.

The solid line pattern of Fig. 4 comprises an equilateral triangle wherein one end of each line forming the sides of the triangle terminates at the junction with the line forming another side and the other end of each line extends beyond its junction with the line forming the. remaining side. Thus, the solid line H terminates at one end at the junction Ila with the line l3 and its other end lib extends beyond its junction Ila with the line forming the remaining side l2.

In accordance with my observations, the lines ii, I! and i3 (Fig. 4) which are simultaneously revealed in the slab comprise or coincide with the three X-axes of the quartz. I have also observed that the projected or extended ends (1. e., the terminals marked lib, l2b, lib) of these lines are the electrically positive ends of the X-axes with which they coincide. Hence, I may mark or otherwise designate each of these ends with a positivesymbol and the opposite ends with a negative symbol for the attention of the lapidary. Further, I have observed that a major side surface of the mother crystal always lies parallel to, and to the right, of each of said lines ll, l2 and I3 when said lines are sighted from a point adjacent their nonextended or negative terminals Ila, Ha, Ha.

Since, as shown in Fig. 6, all unbroken quartz mother crystals are hexagonal pyramids, I am thus able to reconstruct or visualize the original appearance of the mother crystal from which the slab 9 was out. To this end, I may draw lines m 1n and m on the slab parallel to the lines ll, l2 and i3, respectively, and connect them by the In this case, the lines n will be understood to be parallel to the minor side faces of the mother crystal.

(As will be appreciated by those skilled in the art, the ability to locate the virtual location of the major and minor side and apex faces of the quartz specimen is of especial importance to the lapidary in the cutting of resonator and oscillator elements whose electrode faces must be tilted with respect to either a major or minor face.)

The light pattern shown by the solid lines of Fig. 4 will ordinarily be obtained only when the light projected upon the etched side of the specimen is brought to a very fine focus. Such a focus could be obtained by means of a suitable condensing lens system, but may be achieved more economically by means of a mask 6 (as shown in Fig. 3) in which case the aperture 1 should be clean-cut and preferably about the diameter of an ordinary straight pin. An increase in the size of the spot may change the form of the pattern.

By way of example, referring to Fig. 5, a pattern comprising three radially extending lines 2 l,

22 and 23, each 120 apart will be obtained when a slightly larger spot of light impinges the central or Z-axis of the slab. If the light is directed to a point on the slab away from its center, these lines will ordinarily not appear to meet if drawn to a common point (as they do in Fig. but will extend outwardly toward the edges of the slab,

as if from a triangle (see Fig. 4) whose sides are formed by extending the said lines inwardly toward each other. In either event, and as described in connection with Fig. 4, these lines comprise or coincide with the X-axes of the quartz,

the positive terminals of these X-axes are in the (outward) direction of extension of the said axes. and a line drawn parallel to and to the right of each of these axes as viewed by an observer looking along the axes in the direction of said positive terminals comprises the virtual major (M) faces of the quartz.

I claim:

1. Method of locating the X-axes, the positive terminals of said X-axes, and the virtual location of the major faces of an irregular quartz slab having its principal surfaces lying in substantially parallel planes normal to the Z-axis, said method comprising etching one of said surfaces, directing a spot of light upon said etched surface to produce a pattern of light comprising three lines being substantially 120 apart adjacent the opposite surface of said slab, observing the direction of extension of each of said lines from the point at which each line intersects another of said lines marking the said three lines and the terminals thereof on said slab as X-axes whose positive terminals are in the direction of extension of said lines, drawing on the slab a line parallel to and to the right of each of the said X-axes as viewed by an observer at the negative terminals thereof looking in the direction of said positive terminals, and marking the three lines thus drawn as the virtual major faces of the quartz.

2. Method of locating the X-axes of a quartz slab having its principal surfaces lying in substantially parallel planes normal to the Z-axis, said method comprising etching one of said surfaces, directing a spot of light upon said etched surface to produce a pattern of light comprising three lines visible from the opposite surface of said slab, and marking on the slab the said lines as the X-axes.

3. Method of determining the location and polarity of a quartz slab having its principal surfaces lying in substantially parallel planes nor-' mal to the Z-axis, said method comprising etching one of said surfaces, directing a spot of light upon said etched surface to produce a pattern of light comprising three lines lying substantially apart and visible from the opposite surface of said slab, observing the direction of extension of each of said lines from the point at which each line intersects another of said lines, and marking said lines and the terminals thereof on said slab as X-axes whose positive terminals are in the direction of extension of said lines.

4. Method of simultaneously locating the three X-axes of a quartz slab having its principal surfaces lying in substantially parallel planes normal to the Z-axis, said method comprising etching one of said surfaces, directing a pin-point" of light upon said etched surface to produce a,

substantially triangular light pattern visible to an observer looking into the slab from the opposite surface thereof, and marking on the slab the lines comprising the sides of said triangular light pattern as the three X-axes.

5. Method of simultaneously locating the three X-axes of a quartz slab having its principal surfaces lying in substantially parallel planes normal to the Z-axis, said method comprising etching one of said surfaces, directing upon said etched surface a spot of light of a diameter such as to produce in said quartz a light pattern comprising three substantially radially extending lines, and marking on the slab the said radially extending lines asthe three X-axes.

. HENRY W. N. HAWK. 

